Beams for sector covering transmission in mobile telephony communication systems are in case of array antennas generated by means of beamforming for transmission of user specific information. Examples of standards are TD-SCDMA and LTE-TDD, which both typically use, or will use, dual polarized antennas arranged in four columns.
The idea of combining beams, to generate a compound beam, has been disclosed, see U.S. Pat. No. 5,649,287 (reference [1]), which describes combination of beam ports from antennas having orthogonal polarizations. In [1] is disclosed the combination of beam ports associated with antennas having, not only different polarizations but also, different spatial pointing directions, to achieve a compound beam covering a larger area in an azimuth without creating nulls or near null in the combined antenna pattern.
A prior art antenna, as disclosed in FIG. 1, have two beams with orthogonal polarization covering the same area for the purpose of diversity.
The commonly used method for generating beams by means of a dual polarized array antenna is shown in FIG. 2, where each beam is generated with elements having the same polarization.
The typical problems with the common methods are:                The match between the actual and the desired beam shape is poor, since the created amplitude pattern “ripples” around the desired beam shape pattern, as illustrated in FIG. 3.        The power utilization is inefficient in the sense that the magnitude for the individual elements of the weight vector is not constant.        The weight vectors are antenna specific, i.e. they are designed for a certain element spacing and element beamwidth.        
The patent publication WO2006/071153 discloses an antenna device for a radio base station in a cellular telephony system. A further patent publication WO2010/006645 discloses a base station repeater station pair.
Thus there is a need for an improved method for designing weight vectors for dual beam antennas with orthogonal polarizations.